In animals, mtDNA is always transmitted through the female and this is termed “maternal inheritance.” Recently, autophagy was reported to be involved in maternal inheritance by elimination of paternal mitochondria and mtDNA in Caenorhabditis elegans ; moreover, by immunofluorescence, P62 and LC3 proteins were also found to colocalize to sperm mitochondria after fertilization in mice. Thus, it has been speculated that autophagy may be an evolutionary conserved mechanism for paternal mitochondrial elimination. However, by using two transgenic mouse strains, one bearing GFP-labeled autophagosomes and the other bearing red fluorescent protein-labeled mitochondria, we demonstrated that autophagy did not participate in the postfertilization elimination of sperm mitochondria in mice. Although P62 and LC3 proteins congregated to sperm mitochondria immediately after fertilization, sperm mitochondria were not engulfed and ultimately degraded in lysosomes until P62 and LC3 proteins disengaged from sperm mitochondria. Instead, sperm mitochondria unevenly distributed in blastomeres during cleavage and persisted in several cells until the morula stages. Furthermore, by using single sperm mtDNA PCR, we observed that most motile sperm that had reached the oviduct for fertilization had eliminated their mtDNA, leaving only vacuolar mitochondria. However, if sperm with remaining mtDNA entered the zygote, mtDNA was not eliminated and could be detected in newborn mice. Based on these results, we conclude that, in mice, maternal inheritance of mtDNA is not an active process of sperm mitochondrial and mtDNA elimination achieved through autophagy in early embryos, but may be a passive process as a result of prefertilization sperm mtDNA elimination and uneven mitochondrial distribution in embryos.

Background: Maternal obesity has adverse effects on oocyte quality, embryo development, and the health of the offspring.Objectives: To understand the underlying mechanisms responsible for the negative effects of maternal obesity, we investigated the DNA methylation status of several imprinted genes and metabolism-related genes.Methods: Using a high-fat-diet (HFD)-induced mouse model of obesity, we analyzed the DNA methylation of several imprinted genes and metabolism-related genes in oocytes from control and obese dams and in oocytes and liver from their offspring. Analysis was performed using combined bisulfite restriction analysis (COBRA) and bisulfite sequencing.Results: DNA methylation of imprinted genes in oocytes was not altered in either obese dams or their offspring; however, DNA methylation of metabolism-related genes was changed. In oocytes of obese mice, the DNA methylation level of the leptin (Lep) promoter was significantly increased and that of the Ppar-α promoter was reduced. Increased methylation of Lep and decreased methylation of Ppar-α was also observed in the liver of female offspring from dams fed the high-fat diet (OHFD). mRNA expression of Lep and Ppar-α was also significantly altered in the liver of these OHFD. In OHFD oocytes, the DNA methylation level of Ppar-α promoter was increased.Conclusions: Our results indicate that DNA methylation patterns of several metabolism-related genes are changed not only in oocytes of obese mice but also in oocytes and liver of their offspring. These data may contribute to the understanding of adverse effects of maternal obesity on reproduction and health of the offspring.Citation: Ge ZJ, Luo SM, Lin F, Liang QX, Huang L, Wei YC, Hou Y, Han ZM, Schatten H, Sun QY. 2014. DNA methylation in oocytes and liver of female mice and their offspring: effects of high-fat-diet–induced obesity. Environ Health Perspect 122:159–164; http://dx.doi.org/10.1289/ehp.1307047

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